基于油水渗流规律分析油水界面深度差异主控因素——以渤海南堡35-2油田为例

摘要

In actual reservoir,the phenomena that the depth of oil-water contact is different in the same sedimentary unit and oil-water contact is not parallel with structural contour are very common.Taking NB35-2 oilfield as an example,according to the principle of gravity differentiation of structural oil and gas reservoirs,oil and gas migration-accumulation is studied by using the theory of equilibrium between the driving force and resisting force of petroleum accumulation,and the primary causes of oil-water contact depth difference are analyzed based on the exploration and exploitation achievements.The study shows that depth difference of oil-water contact is closely related to the process of oil and gas generation,migration,accumulation and losses.The process from hydrocarbon generation to depletion can be divided into reservoir formation stage and reservoir adjustment stage,and in different stages the force balance is different:①in the reservoir formation stage,the area with greater charging pressure,less oil and water density difference and updip formation has higher oil column height,causing the differential distribution of oil-water contact;②in the reservoir adjustment stage,the degree of hydrocarbon depletion affects the depth of oil-water contact.When sand thickness is larger than critical oil column height (buoyancy force equals capillary pressure),oil and gas can form secondary reservoir by overcoming capillary pressure,thus reducing oil-water contact and forming differential depth.The results can guide oilfield development and improve the theoretical understanding in this field.%在实际油藏中,同一沉积单元油水界面存在深度差异、油水界面与构造线不完全平行的现象十分普遍.以渤海南堡35-2油田为例,利用构造油藏成藏重力分异的物理学原理,根据非均质油藏成藏动力与成藏阻力之间的平衡关系以及油水渗流规律,判断储集层中油的运聚状态,并利用油田勘探开发实践成果对油水界面存在深度差异的原因进行了分析.研究表明,油水界面深度差异的形成与油气生成、运移、聚集再到散失的过程密切相关,可将油气生成到散失的全过程分为油藏形成阶段和油藏调整阶段,不同阶段油气的受力不同,导致油水界面深度差异的主控因素也不同:①油藏形成阶段,油气充注压力越大、储层物性越好、油水密度差越小、地层上倾的区域具有更大的油柱高度,从而导致油水界面的差异分布;②油藏调整阶段,油气的散失程度影响油水界面的深度,砂体厚度超过临界油柱高度(即浮力与毛细管阻力相等时的油柱高度)时,油气可以克服毛细管阻力运移至浅层形成次生油藏,从而造成油水界面上升形成深度差.本文研究成果对指导油田开发挖潜,乃至完善该方面理论认识都具有重要意义.